In general, an outboard engine of this type is supported by a swivel bracket and can be turned right and left on a roughly vertical steering axis to steer the vessel. The swivel bracket is positioned between a pair of clamp brackets. It is possible to steer the vessel by turning the steering wheel of a steering apparatus, which includes either a mechanical device or a hydraulic device of the cantilever type or both-end support type.
The mechanical device has a push-pull cable, which includes an outer cable and an inner cable. The outer cable is connected to one end of a guide tube, which extends along a horizontal tilting axis through the clamp and swivel brackets. The inner cable extends through the guide tube, protrudes from its other end is connected through a link to a steering lever, which is fixed to the engine housing. Because the pushing force and pulling force transmitted by the inner cable are limited, the mechanical device is used for an outboard engine having relatively low horsepower.
The hydraulic device of the cantilever type has a hydraulic cylinder and a horizontal piston rod. One end of the hydraulic cylinder is fitted to one end of a guide tube, which extends along a horizontal tilting axis through the clamp and swivel brackets. One end of the piston rod is connected through a link to a steering lever, which is fixed to the engine housing. Because the moment exerted on the link is limited, this hydraulic device as well is used for an outboard engine having relatively low horsepower.
As stated above, a push-pull cable is connected to only one end of the guide tube, or one end of a hydraulic cylinder is fixed to only one end of the tube. This causes no inconvenience because the thread of one end of the guide tube is standardized in outer diameter.
The hydraulic device of the both-end support type is used for an outboard engine having high horsepower. This hydraulic device as well has a hydraulic cylinder and a horizontal piston rod. Both ends of the piston rod are supported by a pair of arms, which is fitted to a guide tube. The guide tube extends along a horizontal tilting axis through the clamp and swivel brackets. The hydraulic cylinder slides along the piston rod to steer the vessel.
Against such a background, the outboard engines made by different makers are so standardized that one end (generally the starboard end) of each guide tube has an external thread that is ⅞ inch in outer diameter. Each maker sets its own outer diameter of the external thread of other end, which may be ⅞ inch or 20 mm.
One end of the guide tube is fitted with a cylindrical nut fit for the ⅞ inch thread. The cylindrical nut makes it possible to fit the push-pull cable or the hydraulic cylinder of the cantilever device smoothly to this end of the guide tube.
One arm of the hydraulic device of the both-end support type is fitted to one end of the guide tube by fittings including a cylindrical nut fit for the ⅞ inch thread. However, before the other arm is fitted to the other end of the guide tube, it is necessary to buy fittings fit for this tube. It is inconvenient and may take a long time to buy the fittings. Even if fittings are bought, they may not be fit for the guide tube.
FIG. 7 of the accompanying drawings shows a steering apparatus including a hydraulic device of the both-end support type. This hydraulic device has a horizontal hydraulic cylinder 26, through which a piston rod 25 slides. Each end of the piston rod 25 is supported by the front end of an arm 23, the rear end of which is supported turnably by one end of a guide tube 48. The guide tube 48 extends along a horizontal tilting axis through a pair of clamp brackets 42 and a swivel bracket 41. The clamp brackets 42 are fixed to the hull (stern) of a boat. The swivel bracket 41 is positioned between the clamp brackets 42 and has a central recess 43 formed in its front end. The hydraulic cylinder 26 is connected through a steering link 47 to the front end of a steering lever 46, which is fixed to the housing of an outboard engine 40.
The guide tube 48 has external threads 48a and 48b cut in both its ends, which engage with cylindrical nuts 31. Each cylindrical nut 31 includes a sleeve 32. Each arm 23 has a bearing hole 23a cut through its rear end, through which the associated sleeve 32 extends so that the arms 23 can pivot on the tilting axis. A nut 34 engages with the outer end of each sleeve 32.
A similar steering apparatus is disclosed in Japanese unexamined patent publication No. 2002-331997 (paragraphs 0017–0019 and FIGS. 1–3).
As stated above, an arm is fitted to each end of the guide tube. In this case, each of the makers of outboard engines sets its own outer diameter of the thread of one end of the guide tube. This makes it necessary to order exclusive fittings after knowing the maker of the outboard engine for which the steering apparatus is to be used. It may take a long time to buy the fittings, and wrong fittings may be bought.
The arms extend from the guide tube on the tilting axis backward and toward the hull. The rear ends of the arms support the piston rod, which supports the hydraulic cylinder. As a result, great moments are exerted on the arms. For this reason, the arms and other parts need to have high strength. This makes the steering apparatus complex in structure and heavy.